A good example of this theory in action is Roger Bannister running the first sub-four-minute mile. For nine years, the record had stood at 4:01.3, but after Bannister dipped below the mythical barrier, running 3:59.4 in 1954, some 200 other athletes followed suit within a year.
For Bart Bailey, 36, now a seven-time London Marathon finisher and in training for number eight, Bandura's theory was the catalyst to his marathon running.
"I grew up in the 1980s, when we had some amazing British marathon runners, including Steve Jones who won New York, and Hugh Jones and Charlie Spedding who won London. They inspired me to want to run a marathon too, but I thought it would be impossible. Then, in my late 20s, I started to meet people who'd managed it. Suddenly, something that had seemed so far beyond my capabilities felt within my reach."
Hard...but not too hard
More people running marathons means...well, even more people running marathons. But they aren't running them because they're easy; quite the opposite. The key here lies in the balance between 'hard' and 'too hard', because it seems the marathon occupies exactly the right spot on this scale.
Sports psychologist Dr Victor Thompson believes the marathon is "a significant enough challenge that you have to train seriously, but it's still doable by us mere mortals with the right amount of commitment over a long enough period".
The key factor in the marathon's length is that it's far enough to push the average body to its first major biological breakdown, yet not so far that finishing becomes an impossibility.
Hitting 'the wall'
Because the average body can only store enough fuel for 18-20 miles of running, there comes a very obvious point in a marathon where almost everyone wants to give up as they run out of gas and 'hit the wall'.
Gareth Evans, sports scientist and strength and conditioning coach at the Porsche Human Performance Centre in Silverstone, explains what's happening at this point: "It's a combination of things, but 'hitting the wall' is primarily about running out of glycogen, the major fuel for exercise. Elite athletes train to avoid this by teaching their bodies to take energy from fat stores, but for most people this doesn't happen fast enough, no matter how much fat they have to burn.
As well as running on empty at this point, runners will also have raised core temperatures and fatigue to their central and peripheral nervous systems, as well as sore and swollen muscles to contend with. So from every angle, the body is yelling at them to stop."
Energy gels, drinks and bars all help with this. But even so, the misery of hitting the wall on top of muscle pain, cramps, and blisters makes this section of the marathon a killer hurdle. If there were another 20 miles to the finish, it would be too much for most people; but with just six or so to go, the incentive to push on is often strong enough to win the battle.
The event is basically everything your body can possibly manage, then a little bit more. For those who do make that finish, this only adds to the enormous satisfaction of marathon running, and it's yet another reason we're so obsessed with this event.
Running a marathon lets us take control of our lives. As Firth-Clark says, "We all like to set goals and achieve them, but life doesn't always let us do that. But with a marathon, runners can take full control of their own destiny, set a high goal, then see it through to the end. This makes marathon running hugely satisfying, both mentally and physically."
Then there's the popular perception of the marathon as being incredibly tough, and this helps it occupy the fabled place it does for so many runners. It's a perception that has been honed over the years and has brought the event into popular consciousness.
Pheidippides' untimely death might have been the legend that kicked it all off, but by the late 1970s, mass participation marathons like New York were initiating a change in marathon running, proving this wasn't an event confined to elites only. With TV sports coverage growing at the same time, these city marathons made a natural spectacle. This coverage spread the marathon fever once again.
Now with four marathons under his belt, 36-year-old David Hunstone was one of thousands who caught the bug after seeing the marathon on TV. "I must have been 10 years old, and I remember it vividly," he says. "I didn't know much about what I was seeing but I knew it was a marathon and it looked amazing. I was fascinated by it and knew I wanted to run one when I was older."